This invention relates to a power steering apparatus for a vehicle with a so-called rotary type changeover valve having a valve housing provided therein with a rotary type valve body arranged to be turned in either one direction or another by a turning operation of a steering shaft. An oil supply port is connected to an oil pressure pump and is selectively connected to either one or the other of cylinder ports connected to left and right chambers, respectively, of a power cylinder.
It has been usual hitherto with this kind of apparatus that it is provided with such an oil pressure reaction chamber mechanism that, at the time of power assistance caused by supply of the pressure oil to the power cylinder, that the changeover valve be pushed back towards its neutral position by oil pressure corresponding to a road surface resistance (a steering reaction force acting on a tire) generated at the cylinder. Thereby a driver can be given a steering feeling in proportion to the road surface resistance. If, for this purpose, a spool type valve is used as the changeover valve, an oil pressure reaction chamber can be formed by using the front and rear end portions in the slide movement direction of the spool valve body as pressure receiving surfaces, so that the oil pressure reaction chamber can be formed comparatively small in size and simple in construction. If, however, a rotary type valve is used as the changeover valve, because the rotary type valve body itself does not have any pressure receiving surface for returning it towards its neutral position, pressure receiving surfaces and an oil pressure reaction chamber have to be provided separately therefrom, so that the apparatus is liable to become large in size and complicated in construction, and thus there has not been proposed as yet any one suitable for practical use.